This has been a problem almost since the queue was introduced many many months ago, and I remember it being discussed here before, but I can't find the thread anymore to bump it, and it's still not fixed, so I thought I'd point it out again...

When you watch a "short" episode (series such as "Ai Mai Mi", "Mangirl" or "Boku no Imouto wa Osaka-okan") where the duration of the episode is less than 5 minutes, the show doesn't update to show that it's been watched in your queue the first time you watch it. If I go back and watch it again a second time, it resumes from the 2 minute mark (instead of at the begining) and THAT time it does mark as watched.

The main drawback of this is it makes it hard to tell when the next episode comes out by looking at your queue, because you still have the previous episode sitting there as "partially watch" instead of the "Coming Soon" block you would normally have when the next one isn't there yet.

This occurs when there is not a place holder for the next episode. If there is a placeholder already in place, a short episode updates correctly for me. If there isn't, then it does exactly as you describe.

Ai Mai Mi just came out, so I got screenshots to demonstrate as I reproduced it, just in case they're useful (thanks for passing it along!)

This really comes down to a matter of timing. For this particular series each episode is 3 minutes long which can lead to more problems than others. The site is not told what second you are at every second because that would be ridiculous, but it doesn't just say beginning and end either because then it couldn't let you continue where you left off. Instead it reports it every ~30 seconds (actual time varies) and then it changes to ~60 seconds. Using Ai Mai Mi as an example, it reports your time at 30 s, 60 s, 120 s, and finally at 180 s. That last one just happens to coincide with the end of the show. If the episode ends and it does not tell the website the time at 180 s then it still thinks the farthest you have watched is 120 s or the 2 minute mark, not far enough to count as having finished the episode.

I watched all of the episodes in order to see if I could reproduce the problem myself. Only once did it happen, but I think that was more a problem with my slow internet. If I had to suggest an easy fix, I would say add one second to the end of each episode. That way they don't have to change any of the video player's code that might affect other series. Regardless, it might take some time to fix.

Does it happen consistently with you or only sometimes? Are you running any other programs at the same time that are using any network resources?

happens pretty consistently with me, and I was guessing exactly what you said for how it's probably reporting it. The easy fix of course is to make it so it specifically reports in when it hits the end of the episode, instead of waiting for the next 60 second mark or whatever.